1. Field of the Invention
The present invention relates to an exhaust gas recirculation system (EGR system) incorporated into an internal combustion engine to recirculates part of the exhaust gas discharged from the internal combustion engine at a controlled flow controlled by a recirculation control valve to an intake passage and, more specifically, to the construction of a flow passage connecting an exhaust passage and the recirculation control valve.
2. Description of the Related Art
A conventional internal combustion engine is provided with an exhaust gas recirculation system for recirculating part of the exhaust gas to an intake passage to suppress the generation of NOx by lowering maximum combustion temperature and to improve fuel consumption by reducing pumping loss. In the exhaust gas recirculation system, a recirculation control valve for controlling the flow of the recirculation exhaust gas is attached to the cylinder head of the internal combustion engine, and a recirculation exhaust gas inlet through which part of the exhaust gas flowing through an exhaust passage is extracted is formed in an exhaust manifold or an exhaust pipe connected to the lower end of the exhaust manifold.
When the recirculation exhaust gas inlet is formed in a lower part of the exhaust manifold, the exhaust pipe or a part of the exhaust pipe below a part of the exhaust pipe where a catalytic converter is placed, the recirculation exhaust gas inlet is at a relatively lower position on the exhaust passage with respect to the flowing direction of the exhaust gas. Therefore, a relatively long recirculation passage is needed to connect the exhaust gas passage and the recirculation control valve attached to the cylinder head. Thus the recirculation exhaust gas taken out of the exhaust passage dissipates heat into the atmosphere and is subject to cooling while the same flows through the recirculation passage to the recirculation control valve. Consequently, carbon and hydrocarbons (HC) contained in the recirculation exhaust gas are not oxidized and deposit deposits including carbon on the valve element of the recirculation control valve and in the gas passage of the recirculation control valve. The deposits in the passages obstruct the flow of the recirculation exhaust gas and make the recirculation control valve unable to function properly for flow control.
Heat dissipation while the recirculation exhaust gas is flowing through the recirculation passage may be reduced by reducing the length of the recirculation passage. However, the length of the recirculation passage cannot be reduced below a minimum necessary length dependent on the positional relation between the recirculation gas outlet and the recirculation control valve. Even if the recirculation passage is formed in the shortest possible length, the recirculation exhaust gas is still apt to dissipate heat into the atmosphere and to be cooled. Thus the reduction of the length of the recirculation passage cannot be an effective means for suppressing the deposition of deposits on the recirculation passage.
The present invention has been made in view of such circumstances and it is therefore an object of the present invention to provide an exhaust gas recirculation system of simple construction capable of suppressing the drop of the temperature of a recirculation exhaust gas flowing through a recirculation passage between an exhaust passage and a recirculation control valve and of suppressing the deposition of deposits including carbon on the components of the recirculation control valve.
Another object of the present invention is to provide an exhaust gas recirculation system for a multicylinder internal combustion engine having a plurality of cylinders, capable of preventing the extraction of part of an exhaust gas from an exhaust passage as a recirculation exhaust gas from making the ratios of effect of the cylinders on a measured value measured by an exhaust gas analyzer placed in the exhaust passage to acquire data for estimating an air-fuel ratio differ from each other.
According to a first aspect of the present invention, an exhaust gas recirculation system includes: a recirculation passage having one end connected to an exhaust passage included in an internal combustion engine and the other end connected to an intake passage included in the internal combustion engine to extract part of an exhaust gas as a recirculation exhaust gas from the exhaust passage and to recirculate the same to the intake passage; and a recirculation control valve placed in the recirculation passage to control the flow of the recirculation exhaust gas into the intake passage; wherein a recirculation pipe forming a part of the recirculation passage has a section extended close to and along an exhaust pipe forming a part of the exhaust passage.
The section, extended close to and along the exhaust pipe, of the recirculation pipe for carrying the recirculation exhaust gas extracted from the exhaust passage to the recirculation control valve is included in an environment heated at a high temperature by the heat radiated by the exhaust pipe heated at a high temperature by the exhaust gas. Therefore, heat dissipation from the recirculation pipe into the atmosphere is small even if the recirculation pipe is long and the drop of the temperature of the recirculation exhaust gas flowing through the recirculation pipe is suppressed. Consequently, the recirculation exhaust gas is maintained at a high temperature, the oxidation of carbon and hydrocarbons contained in the recirculation exhaust gas is promoted and hence the deposition of deposits including carbon on the valve element and the walls of a valve case of the recirculation control valve can be suppressed.
Thus simple construction including the recirculation pipe extended close to the exhaust pipe suppresses the deposition of deposits including carbon in the recirculation control valve and prevents the recirculation control valve from becoming incapable of properly controlling the flow of the recirculation exhaust gas due to the deposition of deposits in the recirculation control valve.
In the exhaust gas recirculation system according to the first aspect of the present invention, both the recirculation pipe of the recirculation passage, and the exhaust pipe of the exhaust passage may be covered with a heat insulating cover. When both the recirculation pipe and the exhaust pipe are covered with the heat insulating cover, a hot atmosphere heated by heat radiated by the exhaust passage is created in a space enclosed by the heat insulating cover. Since the recirculation pipe is extended in the hot atmosphere, the amount of heat radiated by the recirculation pipe into the atmosphere is reduced, the drop of the temperature of the recirculation exhaust gas flowing through the recirculation pipe is suppressed and the oxidation of carbon and hydrocarbons contained in the recirculation exhaust gas is promoted. Consequently, the deposition of deposits including carbon on the valve element of the recirculation control valve and in the exhaust gas passage of the recirculation control valve can be suppressed. Thus simple construction including covering both the recirculation pipe and the exhaust pipe with the heat insulating cover enhances the aforesaid effect of the exhaust gas recirculation system.
According to a second aspect of the present invention, an exhaust gas recirculation system includes: a recirculation passage having one end connected to an exhaust passage included in an internal combustion engine and the other end connected to an intake passage included in the internal combustion engine to extract part of an exhaust gas as a recirculation exhaust gas from the exhaust passage and to recirculate the same to the intake passage; and a recirculation control valve placed in the recirculation passage to control the flow of the recirculation exhaust gas into the intake passage; wherein the internal combustion engine is mounted on a vehicle, an exhaust pipe forming a part of the exhaust passage is extended on a lower side of an engine body included in the internal combustion engine with respect to the direction of running wind, a recirculation pipe forming a part of the recirculation passage has an upper end connected to a part, facing the engine body, of the exhaust pipe, and the recirculation pipe has a heat retaining section extended in a space between the engine body and the exhaust pipe.
In the exhaust gas recirculation system according to the second aspect of the present invention, the heat maintaining section including the upper end of the recirculation pipe is disposed behind the engine body of the internal combustion engine mounted on the vehicle and is screened from the running wind that blows against the running vehicle by the engine body. Thus the heat retaining section is cooled scarcely by the running wind, a space screened from the running wind is formed between the engine body and the exhaust pipe, the space is heated by heat radiated by the exhaust pipe at a high temperature, and the heat retaining section including the upper end of the recirculation pipe is extended in the high-temperature space. Therefore, heat dissipation from the recirculation pipe into the atmosphere is small even if the recirculation pipe is long, the drop of the temperature of the recirculation exhaust gas is suppressed from the moment the recirculation exhaust gas is extracted from the exhaust passage, the oxidation of carbon and hydrocarbons contained in the recirculation exhaust gas is promoted and, hence, the deposition of deposits including carbon on the valve element of the recirculation control valve and in the exhaust gas passage of the recirculation control valve is suppressed.
According to a third aspect of the present invention, an exhaust gas recirculation system includes: a recirculation passage having one end connected to an exhaust passage included in an internal combustion engine and the other end connected to an intake passage included in the internal combustion engine to extract part of an exhaust gas as a recirculation exhaust gas from the exhaust passage and to recirculate the same to the intake passage; and a recirculation control valve placed in the recirculation passage to control the flow of the recirculation exhaust gas into the intake passage; wherein a recirculation pipe forming a part of the recirculation passage has a contact section extended along an exhaust pipe forming a part of the exhaust passage with its outer surface in contact with the outer surface of the exhaust pipe.
In the exhaust gas recirculation system in the third aspect of the present invention, the recirculation pipe has the contact section extended along the exhaust pipe with its outer surface in contact with the outer surface of the exhaust pipe. Therefore heat is transmitted from the exhaust pipe to the contact section, in contact with the exhaust pipe, of the recirculation pipe to suppress the drop of the temperature of the recirculation pipe, the area of the heat radiating surface of the recirculation pipe is reduced by the area of a part of the recirculation pipe in contact with the exhaust pipe, the drop of the temperature of the recirculation exhaust gas flowing through the recirculation pipe is suppressed and the oxidation of carbon and hydrocarbons contained in the recirculation exhaust gas is promoted. Consequently, the deposition of deposits including carbon on the valve element of the recirculation control valve and in the exhaust gas passage of the recirculation control valve is suppressed.
According to a fourth aspect of the present invention, an exhaust gas recirculation system includes: a recirculation passage having one end connected to an exhaust passage included in an internal combustion engine and the other end connected to an intake passage included in the internal combustion engine to extract part of an exhaust gas as a recirculation exhaust gas from the exhaust passage and to recirculate the same to the intake passage; and a recirculation control valve placed in the recirculation passage to control the flow of the recirculation exhaust gas into the intake passage; wherein the recirculation passage has an internal passage section formed inside an exhaust pipe forming a part of the exhaust passage and separated from the exhaust passage by a partition wall formed in the exhaust pipe.
In the exhaust gas recirculation system according to the fourth aspect of the present invention, heat of the exhaust gas flowing through the exhaust pipe is transmitted through the partition wall to the recirculation exhaust gas in the internal passage section. Therefore the drop of the temperature of the recirculation exhaust gas flowing through the recirculation passage is suppressed and the area of the heat radiating surface of the recirculation passage is reduced by an area corresponding to the internal passage section formed by placing the wall in the exhaust pipe. Thus the recirculation exhaust gas flowing through the recirculation passage is heated by the heat of the exhaust gas and heat dissipation from the recirculation passage into the atmosphere is suppressed even if the recirculation passage is long, the drop of the temperature of the recirculation exhaust gas flowing through the recirculation passage is suppressed and the oxidation of carbon and hydrocarbons contained in the recirculation exhaust gas is promoted. Consequently, the deposition of deposits including carbon on the valve element of the recirculation control valve and in the exhaust gas passage of the recirculation control valve is suppressed.
Since the internal passage section of the recirculation passage is formed in the exhaust pipe, a recirculation pipe forming the recirculation passage can be extended in a compact arrangement. Thus, simple construction including the recirculation passage having the internal passage section formed in the exhaust pipe simplifies the piping of an exhaust system, which enables the internal combustion engine to be formed in compact construction.
The internal combustion engine may be a multicylinder internal combustion engine provided with a plurality of cylinders, an exhaust manifold may be connected to the cylinders, an exhaust gas analyzer may be placed in the manifold, and the upper end of the recirculation passage may be positioned below the exhaust gas analyzer with respect to the flowing direction of the exhaust gas.
Since the upper end of the recirculation passage is located below the exhaust gas analyzer with respect to the flowing direction of the exhaust gas, it is possible to prevent the cylinders from exhausting at different rate and the resultant difference between the ratios of effect of the cylinders on a measured value measured by the exhaust gas analyzer.
According to a fifth aspect of the present invention, an exhaust gas recirculation system includes: a recirculation passage having one end connected to an exhaust passage included in an internal combustion engine and the other end connected to an intake passage included in the internal combustion engine to extract part of an exhaust gas as a recirculation exhaust gas from the exhaust passage and to recirculate the same to the intake passage; and a recirculation control valve placed in the recirculation passage to control the flow of the recirculation exhaust gas into the intake passage; wherein a section of a recirculation pipe forming a part of the recirculation passage and a section of an exhaust pipe forming a part of the exhaust passage are combined to form a double-wall pipe structure.
In the exhaust gas recirculation system according to the fifth aspect of the present invention, the heat of the exhaust gas is transferred to the recirculation exhaust gas through an inner wall of the double-wall pipe structure. Therefore, the drop of the temperature of the recirculation exhaust gas flowing through the recirculation pipe can be suppressed, the oxidation of carbon and hydrocarbons contained in the recirculation exhaust gas is promoted and, hence, the deposition of deposits on the valve element of the recirculation control valve and in the exhaust gas passage of the recirculation control valve is suppressed.
Since the section of the recirculation pipe is combined with the section of the exhaust pipe to form the double-wall pipe structure, the recirculation passage is compact and the piping of an exhaust system is simplified, which enables the internal combustion engine to be formed in compact construction.
In the exhaust gas recirculation system according to the fifth aspect of the present invention, the internal combustion engine may be a multicylinder internal combustion engine provided with a plurality of cylinders, an exhaust manifold may be connected to the cylinders, an exhaust gas analyzer may be placed in the manifold, the section of the recirculation pipe forms the inner wall of the double-wall pipe structure, and the upper end of the section of the recirculation pipe forming the inner wall of the double-wall pipe structure corresponding to the upper end of the recirculation passage may be located below the exhaust gas analyzer with respect to the flowing direction of the exhaust gas.
Since the section of the recirculation pipe is the inner wall of the double-wall pipe structure surrounded by an annular section of the exhaust passage, the section of the recirculation pipe is not exposed to the atmosphere and heat is transferred through the entire circumference of the section of the recirculation pipe, the drop of the temperature of the recirculation exhaust gas flowing through the recirculation pipe can be further effectively suppressed, the extraction of the exhaust gas as a recirculation exhaust gas can be prevented from making the ratios of effect of the cylinders on a measured value measured by the exhaust gas analyzer differ from each other, and the exhaust gas analyzer is able to provide data necessary for accurate air-fuel ratio control.
According to a sixth aspect of the present invention, an exhaust gas recirculation system includes: a recirculation passage having one end connected to an exhaust passage included in an internal combustion engine and the other end connected to an intake passage included in the internal combustion engine to extract part of an exhaust gas as a recirculation exhaust gas from the exhaust passage and to recirculate the same to the intake passage; and a recirculation control valve placed in the recirculation passage to control the flow of the recirculation exhaust gas into the intake passage; wherein the exhaust passage is provided with branch exhaust pipes connected to individual exhaust passages of a plurality of cylinders included in the internal combustion engine to carry exhaust gases discharged from the cylinders, and an exhaust gas colleting structure for collecting the exhaust gases discharged from the cylinders, the exhaust gas collecting structure is provided with a recirculation exhaust gas inlet through which part of the exhaust gas is extracted as a recirculation exhaust gas and to recirculate the same to the intake passage, an exhaust gas analyzer for analyzing the exhaust gas to provide data for estimating air-fuel ratio is placed in the exhaust gas collecting structure, and the recirculation exhaust gas inlet is formed at a position below the exhaust gas analyzer with respect to the flowing direction of the exhaust gas.
In the exhaust gas recirculation system according to the sixth aspect of the present invention, the exhaust gas analyzer is placed in the exhaust gas collecting structure to analyze a mixed exhaust gas of the exhaust gases discharged from all the cylinders, the ratios of effect of the cylinders on a measured value measured by the exhaust gas analyzer differ scarcely from each other. Since the recirculation exhaust gas inlet of the exhaust gas recirculation system is formed at a position below the exhaust gas analyzer with respect to the flowing direction of the exhaust gas, it is possible to prevent the cylinders from discharging exhaust gases at different rates and the resultant difference between the ratios of effect of the cylinders on a measured value measured by the exhaust gas analyzer due to the extraction of a large amount of the exhaust gas as the recirculation exhaust gas at a position below the exhaust gas analyzer with respect to the flowing direction of the exhaust gas. Consequently, accurate air-fuel ratio control can be achieved on the basis of the data provided by the exhaust gas analyzer, and the NOx concentration of the exhaust gas can be reduced and fuel consumption can be improved by the recirculation of the exhaust gas.
According to the sixth aspect of the present invention, the interior of the exhaust gas collecting structure may be divided by a partition wall into two intermediate collecting passages connected to two cylinder groups each including the cylinders that do not perform an exhaust stroke successively, and the exhaust gas analyzer may be disposed in a recess formed in the partition wall so as to straddle both the intermediate collecting passages.
Since the exhaust gas analyzer is disposed in the recess formed in the partition wall so as to straddle both the intermediate collecting passages respectively connected to the two groups of the cylinders, the partition wall enhances intake and exhaust efficiencies, the exhaust gas analyzer placed in a branching part of the exhaust passage is able to provide data not significantly affected by difference between the ratios of effect of the cylinders on a measured value measured by the exhaust gas analyzer, and the exhaust gas recirculation system having the exhaust gas analyzer disposed in the recess of the partition wall can be formed in compact construction. Since the exhaust gas analyzer is placed in the recess of the partition wall and a part of the exhaust gas analyzer lies in the partition wall, the exhaust gas analyzer is partly screened from the high-temperature exhaust gas by the partition wall, which extends the life of the exhaust gas analyzer.
In the exhaust gas recirculation system in the sixth aspect of the present invention, the recirculation control valve may be attached to an engine body included in the internal combustion engine, the recirculation exhaust gas inlet may be opened into one of the two intermediate collecting passages.
Thus, since the recirculation exhaust gas inlet opens into one of the two intermediate collecting passages, the recirculation exhaust gas inlet can be formed at a position above the joint of the two intermediate collecting passages with respect to the flowing direction of the exhaust gas, i.e., a position nearer to the engine body, so that the passage between the recirculation exhaust gas inlet and the recirculation control valve can be formed in a short length, heat dissipation of the recirculation gas in the passage can be suppressed and the recirculation gas can be maintained at a comparatively high temperature. Consequently, the deposition of deposits including carbon on the valve element of the recirculation control valve and in the exhaust gas passage of the recirculation control valve can be suppressed, and the clogging of the recirculation control valve by deposits and the resultant incapability of the recirculation control valve for desired flow control operation can be prevented.